arm64: use asm-generic/cacheflush.h

ARM64 needs almost no cache flushing routines of its own.  Rely on
asm-generic/cacheflush.h for the defaults.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
Link: http://lkml.kernel.org/r/20200515143646.3857579-10-hch@lst.de


Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>